In mining operations, the efficient fragmentation and breaking of rock by means of explosive charges demands considerable skill and expertise. The explosive charges are placed in appropriate quantities at predetermined positions within the rock and are then actuated via detonators having predetermined time delays, thereby providing a desired pattern of blasting and rock fragmentation. Traditionally, signals are transmitted to the detonators from an associated blasting machine via non-electric systems employing low energy detonating cord (LEDC) or shock tube. Alternatively, electrical wires may be used to transmit firing signals to electrical detonators or more sophisticated signals to and from electronic detonators. For example, such signalling may include ARM, DISARM, and delay time instructions for remote programming of the detonator firing sequence. Moreover, as a security feature, detonators may store firing codes and respond to ARM and FIRE signals only upon receipt of matching firing codes from the blasting machine. Electronic detonators can be programmed with time delays with an accuracy down to 1 ms or less.
The establishment of a wired blasting arrangement involves the correct positioning of explosive charges within boreholes in the rock, and the proper connection of wires between an associated blasting machine and the detonators. The process is often labour intensive and highly dependent upon the accuracy and conscientiousness of the blast operator. Importantly, the blast operator must ensure that the detonators are in proper signal transmission relationship with a blasting machine, in such a manner that the blasting machine at least can transmit command signals to control each detonator, and in turn actuate each explosive charge. Inadequate connections between components of the blasting arrangement can lead to loss of communication between blasting machines and detonators, and therefore increased safety concerns. Significant care is required to ensure that the wires run between the detonators and an associated blasting machine without disruption, snagging, damage or other interference that could prevent proper control and operation of the detonator via the attached blasting machine.
Wireless detonator systems offer the potential for circumventing these problems, thereby improving safety at the blast site. By avoiding the use of physical connections (e.g. electrical wires, shock tubes, LEDC, or optical cables) between detonators and other components at the blast site (e.g. blasting machines) the possibility of improper set-up of the blasting arrangement is reduced. Another advantage of wireless detonators relates to facilitation of automated establishment of the explosive charges and associated detonators at the blast site. This may include, for example, automated detonator loading in boreholes and automated association of a corresponding detonator with each explosive charge, for example involving robotic systems. This would provide dramatic improvements in blast site safety since blast operators would be able to set up the blasting array from entirely remote locations. However, such systems present formidable technological challenges, many of which remain unresolved. One obstacle to automation is the difficulty of robotic manipulation and handling of detonators at the blast site, particularly where the detonators are not wireless electronic detonators and require tieing-in or other forms of hook up to electrical wires, shock tubes or the like.
Underground mining presents distinct challenges compared to surface mining. For example, the fragmentation and extraction of a body of ore located underground requires careful planning and execution. Typically, the body of ore is accessed via tunnelling, or one or more drives, to expose a face of the ore on at least one side. Boreholes are then drilled into the face, and loaded with explosive charges. Actuation of the charges by means of associated detonators fragments a portion of the rock behind the free face, thereby to expose a new face to be drilled and loaded. Meanwhile, fragmented rock from the initial blast can be removed via the access tunnel for processing. Through repeated cycles of drilling, loading, blasting and extraction, the exposed face retreats into the ore body and fragmented ore is retrieved.
Extraction of the fragmented ore may be performed using driven vehicles or remotely controlled vehicles, but as noted above remotely controlled location of the detonators in the boreholes and their operative association with the explosive charges has yet to be developed.
Whilst simple in nature, underground blasting as described above presents significant technical and organizational challenges. For example, on the technical side, the void created must be structurally sound, and may require internal support to prevent ceiling collapse. To this end, columns or pillars of ore are frequently left in place to assist in providing ceiling support, particularly during the active phase of blasting and extraction of the remaining ore. Thus, portions of the valuable ore body are effectively “left behind” at the underground blast site, at least until the void has been structurally reinforced, reducing the efficiency of the ore extraction process.
The complexity of underground mining operations is further exacerbated by organizational challenges at the mine site. Teams of mine workers must be co-ordinated carefully in order to optimize both mining operations and access to the free face and fragmented rock. For example, different teams may be required to access the free face at different times to drill boreholes, load explosives, set up blasting equipment, extract fragmented rock etc. Each team will need a different set of equipment to effectively perform its designated task, and yet there may be insufficient space at the free face to accommodate more than one team, and associated equipment, at any given time.
Furthermore, fragmented material from one blast, or a void resulting from that blast, may prevent access to the ore body on a remote side of that blast, again meaning that portions of the valuable ore body are effectively “left behind”, at least until the fragmented material has been extracted or access has been otherwise facilitated. Moreover, team movement and co-ordination at the mine site is further complicated by safety concerns. Depending upon the integrity of the rock, or the safety rules at the mine site, it may be a requirement to completely evacuate the mine site of all mining personnel (and perhaps equipment) when blasting takes place. Alternatively, or in addition, it may be necessary to reinforce the remaining rock mass before personnel are allowed to access it for further drilling and blasting. Without such reinforcement, that remaining rock mass may also have to be “left behind”. All of these possibilities further constrain the scheduling of all other operations at the mine site for all working faces.
In addition, it may be difficult to access the retreating face of the ore body. Each blasting cycle requires the substantial removal of fragmented rock before the newly exposed ore face can be drilled and loaded for the next blasting cycle. If the rock fragmentation is inefficient or inappropriate in some way, it may be difficult to fully extract the ore via the access tunnel, and this in turn may delay the extraction process. On occasion, undesirable rock fragmentation or throw may result in the ore body being completely inaccessible from an existing access tunnel, such that a new tunnel must be formed to approach the ore body from a different angle. Clearly, this will delay the extraction process, and increase the costs significantly.
It follows that there is a continuing need in the art for improved blasting methods for underground mining. This need extends to blasting arrangements that employ either wired or wireless communication with detonators and associated components.